Playing Surface and Method of Manufacturing a Playing Surface

ABSTRACT

A playing surface comprising a foam layer ( 1 ) having a top surface and a plurality of downwardly extending energy dissipating projections ( 9 ) and a fibrous carpet layer ( 2 ) overlying the top surface of the foam layer ( 1 ). The plurality of the energy dissipating projections ( 9 ) are arranged to dissipate energy of an impact through deformation to significantly affect a Critical Fall Height of the playing surface. The invention also comprises methods of manufacturing the playing surface.

TECHNICAL FIELD

This invention concerns a playing surface and a method of manufacturinga playing surface. The invention has particular, but not exclusive,application to playing surfaces for use in children's playgrounds orother situations wherein a user could fall from a significant height,such as situations wherein the Critical Fall Height is required to be2.4 metres or more.

BACKGROUND

The surface used for playgrounds and the like must be chosen such thatthe Critical Fall Height matches or exceeds the maximum height fromwhich a user can fall from the play equipment. BS EN 1177 defines theCritical Fall Height test. A 4.6 kg spherical ‘headform’ representing achild's head is dropped from various heights onto a test surface, andthe time the headform is in contact with the surface and its peakdeceleration is measured. A stiffer surface reduces the time a head isin contact with the surface but this has to be balanced with the peakdeceleration, which increases with increases in stiffness.

The Critical Fall Height is the height at which the Head InjuryCriterion (HIC) is 1000. HIC is a measure of the likelihood of headinjury arising from an impact. The HIC is calculated using:

${{HIC} = \left\{ {\left( {t_{2} - t_{1}} \right)\left\lbrack {\frac{1}{t_{2} - t_{1}}{\int_{t_{1}}^{t_{2}}{{a(t)} \cdot \ {t}}}} \right\rbrack}^{2.5} \right\}_{\max}},$

wherein t₁ and t₂ are the initial and final times (t) of the intervalduring which the HIC attains a maximum value, usually a 15 ms interval,and a(t) is the instantaneous acceleration over this interval in unitsof gravitational force (g). At a HIC of 1000, one in six people suffer alife threatening injury.

It is known to increase the thickness of a foam layer of a playingsurface in order to increase the Critical Fall Height achieved by theplaying surface. However, it has been found that increasing thethickness of the foam layer only increases the Critical Fall Height upto a specified limit. For a polypropylene foam tile having a foamdensity of 30 grams per litre, the limit for the Critical fall Heightthat can be achieved through increasing the thickness of the foam isapproximately 2.4 metres. Further increases in the thickness of the foamlayer do not significantly increase the Critical Fall Height of theplaying surface.

Furthermore, to keep the time and cost of installation down, the playingsurface should be kept as shallow as possible to reduce the amount ofexcavating work that needs to be done to lay the playing surface.

SUMMARY

According to a first aspect of the invention there is provided a playingsurface comprising a foam layer having a top surface and a plurality ofdownwardly extending energy dissipating projections and a fibrous carpetlayer overlying the top surface of the foam layer, wherein the pluralityof the energy dissipating projections are arranged to dissipate energyof an impact through deformation to significantly affect a Critical FallHeight of the playing surface.

It has been found that providing appropriately arranged projections onthe bottom of the foam layer may increase the Critical Fall Height ofthe playing surface without having to increase the thickness of the foamlayer, allowing a shallower playing surface to be used. Furthermore,Critical Fall Heights above 2.4 metres can be achieved. The projectionsdeform into the spaces between the projections during an impact todissipate the energy of the impact. Appropriately arranged projectionscan change the profile of how energy is dissipated by the foam layer toincrease the Critical Fall Height of the playing surface.

The arrangement of the plurality of the projections may result in theplaying surface having a Critical Fall Height significantly greater, forexample 10 cm, 20 cm or 1 m greater, than a Critical Fall Height thatwould be achieved with a foam layer of the same material and foamdensity having a flat bottom surface.

It has been found that the size and shape of the projections can affectthe Critical Fall Height of the playing surface. In particular, for thetypical foam densities that are appropriate for a foam layer of aplaying surface, the projections should have a height of at least 10 mmand preferably, between 10 mm and 20 mm. It has been found that the sizeof the projections can affect the performance of the playing surface atdifferent fall heights and it is believed that projections having aheight of between 10 mm and 20 mm give a good balance between theperformance at the lower and higher fall heights.

In one embodiment, the foam layer is expanded polypropylene. The foamdensity may be at least 25 grams per litre and preferably, between 30grams per litre and 40 grams per litre. Foam densities below 25 gramsper litre have a tendency to come apart, in use. Foam densities above 40grams per litre may be too stiff resulting in a Critical Fall Height ofthe playing surface of less than 2.4 metres or requiring thickerprojections to achieve a 2.4 metre Critical Fall Height, if this ispossible at all, resulting in a playing surface having a thickness thatis impractical to use.

In one embodiment, the foam layer has a thickness (excluding theprojections) of between 40 mm and 65 mm. The base needs to be stiffenough to avoid “bottoming out” on the hard supporting surface, such asa concrete surface, when a person falls onto the surface but kept asshallow as possible to reduce the amount of excavating that needs to bedone to lay the surface. A foam layer having a thickness of less than 40mm may be too weak at the typical foam densities used for playingsurfaces, which may result in the foam layer breaking up in use. A foamlayer having a thickness of more than 65 mm may be too stiff at thetypical foam densities used for playing surfaces, the impact of theheadform not penetrating much further than 65 mm and therefore, notbeing dissipated by the projections.

Each projection may have a free end that, in use, contacts a surfacesupporting the playing surface, the projection having a shape thatnarrows towards the free-end. The shape of the projection can affect theprofile of how energy is dissipated by the projections during an impactand it is believed that narrowing projections provide a profile thatreduces peak deceleration and therefore, the HIC value. For example, theprojections may be dome shaped. Dome shaped projections performparticular well in use, however, other shaped projections may be usedsuch as pyramid, tetrahedron, cone, wedge shaped, a frustum of theseshapes or any other suitable shape. The disadvantage of projections thatend in points (such as pyramids, tetrahedrons and cones) that contactthe supporting surface is that the point can break off in use.

In one embodiment, the foam layer may comprise one or more holesextending from the top surface to the bottom surface of the foam layer.The holes may allow water to drain from the top surface of the playingsurface. In addition to dissipating energy, the projections providechannels below the foam layer for water to drain from the area coveredby the playing surface.

The playing surface may comprise a geotextile layer between the foamlayer and the carpet layer. The geotextile layer may protect the foamlayer during laying of the carpet, in particular, the carpet layer maybe formed from rolls/strips of carpet connected together using a hotmelt adhesive and the geotextile layer protects the foam layer beingdamaged from the heat. Furthermore, the geotextile layer may increasethe load bearing capacity of the playing surface, reducing damage to thefoam layer during an impact.

It has been found that moulding a foam layer with a conventional mouldresults in a smooth finish to the foam layer that allows the carpetlayer and geotextile layer to move relative to the foam layer, in use.In a playground such movement of the surface is undesirable.Accordingly, in this embodiment, the top surface of the foam layer maycomprise a rough surface that contacts the geotextile or carpet layer toprovide high frictional resistance to relative movement between thelayers. The rough top surface may comprise a plurality of upwardlyextending projections, for example upwardly extending projections thatproduce a course top surface. It will be understood that the upwardlyextending projections are small relative to the thickness of the foamlayer and the height of the energy absorbing projections, for examplehaving a height of less than 0.5 mm, the upwardly extending projectionshaving minimal impact on the energy absorbing capability of the foamlayer but increasing the frictional resistance of the top surface. Inone embodiment, the projections may be irregular.

In one embodiment, the playing surface may comprise two or more foamlayers, each foam layer having a top surface and a plurality ofdownwardly extending energy dissipating projections. The foam layers maybe stacked consecutively on top of each other. It is believed that theprovision of multiple foam layers will further increase the CriticalFall Height of the playing surface. Furthermore, in an embodiment inwhich holes are provided in each foam layer from the top surface to thebottom surface, the projections provide channels from the holes in onefoam layer to the holes in another foam layer for water to drain.Without the channel between the projections, the drainage holes ofconsecutive layers would have to be aligned, increasing the costs ofinstallation.

The foam layer may comprise a plurality of interlocked tiles, each tilehaving formations for cooperating with formations on the other tiles forinterlocking the tiles together. Forming the foam layer from a pluralityof tiles simplifies laying of the carpet layer. The interlocking of thetiles reduces relative movement between the tiles, in use.

According to a second aspect of the invention there is provided a methodof manufacturing a playing surface comprising forming a foam layerhaving a top surface and a plurality of downwardly extending energydissipating projections, wherein the plurality of the energy dissipatingprojections are arranged such that, when the foam layer is used as partof a playing surface with a fibrous carpet layer overlaying the foamlayer, the plurality of projections dissipate energy of an impactthrough deformation to significantly affect a Critical Fall Height ofthe playing surface.

According to a third aspect of the invention there is provided a methodof laying a playing surface comprising laying a foam layer having a topsurface and a plurality of downwardly extending energy dissipatingprojections and overlaying the foam layer with a fibrous carpet layer,wherein the plurality of the energy dissipating projections are arrangedsuch that, when the foam layer is used as part of a playing surface witha fibrous carpet layer overlaying the foam layer, the plurality ofprojections dissipate energy of an impact through deformation tosignificantly affect a Critical Fall Height of the playing surface.

The plurality of the projections may be arranged such that the playingsurface has a Critical Fall Height of at least 2.4 metres.

The method may comprise providing laying a geotextile layer over thefoam layer and laying the carpet layer over the geotextile layer, thecarpet layer comprising a series of carpet strips connected together bya hot melt adhesive, the geotextile layer arranged to protect the foamlayer form heat used in applying the hot melt adhesive.

DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by example only,with reference to the following drawings, in which:

FIG. 1 is a cross-section of a playing surface according to anembodiment of the invention;

FIG. 2 is a perspective view of a tile of the foam layer of the playingsurface shown in FIG. 1 from above;

FIG. 3 is a perspective view of a tile of the foam layer of a playingsurface shown in FIGS. 1 and 2 from below;

FIG. 4 is a side view of a tile of the foam layer of the playing surfaceshown in FIGS. 1 to 3;

FIG. 5 is a blown-up perspective view of a tile of the foam layer of aplaying surface shown in FIGS. 1 to 4 from above;

FIG. 6 is a blown-up perspective view of a tile of the foam layer of aplaying surface shown in FIGS. 1 to 5 from below;

FIG. 7 is a cross-section of a playing surface according to anotherembodiment of the invention; and

FIG. 8 is a cross-section of a playing surface according to yet anotherembodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to FIG. 1, a playing surface comprises a foam layer 1 and afibrous carpet layer 2 overlying the top surface of the foam layer 1.Located between the foam layer 1 and the carpet layer 2 is a geotextilelayer 3.

The fibrous carpet layer 1 comprises a pile (e.g. a yarn that stands upfrom the backing), which may be considered synthetic grass. For example,the pile of the carpet layer may be polypropylene needle punched surfacehaving a 12 to 14 mm pile (14 to 16 mm total thickness including thebacking). The pile may have an open fibrous structure having randomlyoriented fibres, as described in European Patent No: 0174755.

The geotextile layer 3 may be 2 mm thick needle punched polyestermaterial.

The foam layer 2 comprises a plurality of interlocked tiles 5 (one ofwhich is shown in FIGS. 2 to 6), each tile having connecting formations,in this embodiment trapezoidal recesses 4 for cooperating withcorresponding trapezoidal protrusion 6 on the other tiles, forinterlocking the tiles 5 together. Each tile 5 has a top surface 7 and abottom surface 8.

The top surface 8 has a rough texture that contacts the geotextile layer3 to provide high frictional resistance to relative movement between thefoam layer 1 and the geotextile layer 3. The high frictional resistancemay prevent movement of the geotextile layer 3 or carpet layer 2relative to the foam layer 1 when subjected to lateral forces.

The foam layer 1 further comprises a plurality of downwardly extendingenergy dissipating projections 9. The projections 9 are of a shape, inthis embodiment dome shaped, such that the projections 9 narrow towardsa free end 11 (in this embodiment an apex 11 of the dome) that contactsa surface supporting the playing surface. It will be understood that inother embodiments, other shapes may be used for the projections 9. Theprojections 9 have a height (the vertical distance from a valley betweenthe projections to the apex 11 of the projections 9) of approximately 15mm and, in this embodiment in which the projections 9 have a dome shapea diameter of approximately 30 mm. The projections 9 are arranged in apseudo-hexagonal packing arrangement with each projection 9 being closeto but being spaced from adjacent projections 9 by a predetermineddistance, as indicated by rings 11 around each projection 9. It will beunderstood that rings 11 are included in the drawings to illustrate thatthe projections 9 do not meet and these regions are flat and are part ofthe valley between the projections 9.

In this embodiment, the foam layer 1 is expanded polypropylene having afoam density of 30 grams per litre and the thickness of the foam layerfrom the top surface to a valley of the bottom surface is 40 mm.

In one embodiment, the foam layer 1 may comprise one or more holes (notshown) extending from the top surface 7 to the bottom surface 8 thatallow water to drain from the playing surface. The projections 9 providechannels below the foam layer 1 for water to drain from the area coveredby the playing surface.

A combination of foam density of the foam layer 1 and an arrangement ofthe plurality of the projections 9 significantly affects a Critical FallHeight of the playing surface. In particular, the projections 9 arearranged to deform into the spaces to dissipate energy during an impact.It has been found that the combination of features of the foam layer 1of the above-described embodiment results in the playing surface havinga Critical Fall Height of up to 1.4 metres.

Referring to FIG. 7, there is shown another embodiment of a playingsurface according to an embodiment of the invention. In this embodiment,the foam layer 1 has a thickness of 65 mm. The Critical Fall height ofthis playing surface may be at least 2.4 metres.

FIG. 8 shows another embodiment of a playing surface according to theinvention. In this embodiment, the playing surface comprises two foamlayers 1′ and 1″ stacked consecutively on top of each other. It isbelieved that the provision of multiple foam layers further increasesthe Critical Fall Height of the playing surface.

To manufacture the playing surface, the carpet layer 2 and thegeotextile layer 3 may be manufactured in a conventional manner. Thefoam layer 1 is manufactured by moulding the foam layer 1 in a suitablyshaped mould, for example by injection moulding. During the mouldingprocess, the top surface 7 is formed with a rough texture of relativelysmall projections.

Laying of the playing surface is typically carried out by digging out arecess in the ground and, optionally, lining the ground with stone, thestone providing a level supporting surface. The tiles forming the foamlayer 1 are then placed on the stone surface, the tiles beinginterlocked together by recesses 4 and protrusions 6, such that at leastthe apexes (free ends) of the projections 9 contact the stone. Sheetsforming the geotextile layer 3 are placed over the foam layer 1 androlls of carpet layer 2 are placed over the geotextile layer 3. Therolls of carpet may be secured together at the joints by introducingusing a hot-melt adhesive at the seams. It has been found that thegeotextile layer 3 advantageously protects the foam layer 1 from theheat used in this process.

The playing surface of this embodiment is suitable for external use,such as on children's playgrounds.

The table below shows the results of measurements of HIC for a playingsurface according to the invention having 15 mm energy absorbingprojections and a playing surface having a foam tile with no energyabsorbing projections.

Type of Foam Tile Fall Height HIC 50 mm tile with no energy absorbingprojections 2.10 m 897 50 mm tile with 15 mm energy absorbing  2.3 m 801projections Two 50 mm tiles with no energy absorbing 2.45 m 949projections placed one on top of the other Two 50 mm tiles with 15 mmenergy absorbing  3.6 m 767 projections placed one on top of the other

As can be seen from the table, the playing surfaces with foam tileshaving the 15 mm projections can achieve a lower HIC value for higherfall heights. Accordingly, these measurements show that the energyabsorbing projections affect the Critical Fall Height of the playingsurface.

It will be understood that the invention is not limited to theabove-described embodiments, but modifications and alterations can bemade thereto without departing from the aspects of the invention asdefined herein.

For example, the foam layer may be made of other suitable materials,such as polyurethane, expanded polyethylene and expanded polystyrene.

Rather than forming the foam layer 1 with an integral rough top surface7, a separate additional layer may be adhered to the top surface of thefoam layer, this additional layer having an upper surface that providesa high frictional resistance to movement of the geotextile layer 3.

1. A playing surface comprising a foam layer having a top surface and aplurality of downwardly extending energy dissipating projections and afibrous carpet layer overlying the top surface of the foam layer,wherein the plurality of the energy dissipating projections are arrangedto dissipate energy of an impact through deformation to significantlyaffect a Critical Fall Height of the playing surface.
 2. A playingsurface according to claim 1, wherein at least two of the plurality ofprojections have a height of at least 10 mm.
 3. A playing surfaceaccording to claim 2, wherein the majority, if not all, of the pluralityof projections have a height of at least 10 mm.
 4. A playing surfaceaccording to claim 2, wherein the plurality of projections have a heightof between 10 mm and 20 mm.
 5. A playing surface according to claim 1,wherein the arrangement of the plurality of the projections results inthe playing surface having a Critical Fall Height significantly greaterthan a Critical Fall Height that would be achieved with a foam layer ofthe same material and foam density having a flat bottom surface.
 6. Aplaying surface according to claim 1, wherein the foam layer is expandedpolypropylene.
 7. A playing surface according to claim 1, wherein thefoam density is at least 25 grams per litre.
 8. A playing surfaceaccording to claim 7, wherein the foam density is between 30 grams perlitre and 40 grams per litre.
 9. A playing surface according to claim 1,wherein the foam layer has a thickness of between 40 mm and 65 mm.
 10. Aplaying surface according to claim 1, wherein each projection has a freeend that, in use, contacts a surface supporting the playing surface, theprojection having a shape that narrows towards the free-end.
 11. Aplaying surface according to claim 10, wherein the projections are domeshaped.
 12. A playing surface according to claim 1, wherein the foamlayer comprises one or more holes extending from the top surface to thebottom surface of the foam layer.
 13. A playing surface according toclaim 1 comprising a geotextile layer between the foam layer and thecarpet layer.
 14. A playing surface according to claim 1, wherein thetop surface of the foam layer comprises a rough surface that contactsthe geotextile or carpet layer to provide high frictional resistance torelative movement between the layers.
 15. A playing surface according toclaim 14, wherein the top surface of the foam layer comprises upwardlyextending projections having a height of less than 0.5 mm.
 16. A playingsurface according to claim 1, comprising two or more foam layers, eachfoam layer having a top surface and a plurality of downwardly extendingenergy dissipating projections.
 17. A playing surface according to claim16, wherein the foam layers are stacked consecutively on top of eachother.
 18. A playing surface according to claim 1, wherein the foamlayer comprises a plurality of interlocked tiles, each tile havingformations for cooperating with formations on the other tiles forinterlocking the tiles together.
 19. A method of manufacturing a playingsurface comprising forming a foam layer having a top surface and aplurality of downwardly extending energy dissipating projections,wherein the plurality of the energy dissipating projections are arrangedsuch that, when the foam layer is used as part of a playing surface witha fibrous carpet layer overlaying the foam layer, the plurality ofprojections dissipate energy of an impact through deformation tosignificantly affect a Critical Fall Height of the playing surface. 20.A method of laying a playing surface comprising laying a foam layerhaving a top surface and a plurality of downwardly extending energydissipating projections and overlaying the foam layer with a fibrouscarpet layer, wherein the plurality of the energy dissipatingprojections are arranged such that, when the foam layer is used as partof a playing surface with a fibrous carpet layer overlaying the foamlayer, the plurality of projections dissipate energy of an impactthrough deformation to significantly affect a Critical Fall Height ofthe playing surface.
 21. A method according to claim 19 or claim 20,wherein the plurality of the projections are arranged such that theplaying surface has a Critical Fall Height of at least 2.4 metres.
 22. Amethod according to claim 20, comprises laying a geotextile layer overthe foam layer and laying the carpet layer over the geotextile layer,the carpet layer comprising a series of carpet strips connected togetherby a hot melt adhesive, the geotextile layer arranged to protect thefoam layer from heat used in applying the hot melt adhesive.